1. Field of the Invention
The present invention relates generally to audio conferencing, and more particularly to systems, methods, and devices for improving speaker performance in a small-scale design.
2. Description of the Related Art
The frequency range of human hearing is generally considered to be between approximately 20 Hz and approximately 20 kHz. Human speech typically falls within the range of approximately 100 Hz to approximately 8 kHz. In conventional telephony, the frequency band is truncated outside a range from approximately 300 Hz to approximately 3400 Hz. More recently developed technologies such as VoIP (Voice over Internet Protocol), however, allow for a wider frequency range.
To produce low frequencies, a driver typically needs to have a sufficiently large diaphragm and enough mass to resonate at a low frequency. To produce high frequencies, a driver typically needs to have a sufficiently small diaphragm and a low mass. Woofers are the largest drivers, and are designed to produce low-frequency sounds. Tweeters are much smaller units, designed to produce the highest frequencies. A tweeter usually has a sealed back, while a woofer usually has an open back. With a sealed back, the tweeter creates sound waves on the front side only, while a woofer creates sound waves on both its front and back sides. Midrange drivers are typically used in multi-way speakers with three or more driver sizes. Some midrange drivers have open backs, and while some have sealed backs.
A basic prior-art speaker driver 100 with an open back is depicted in FIG. 1. The speaker driver 100 comprises a chassis 102 having a plurality of openings 104. The speaker driver 100 further comprises a diaphragm 106 attached to a suspension 108, which is attached to the chassis 102. The diaphragm 106 is attached to a voice coil 110 which is attached to the chassis 102 by a spider. Each end of the voice coil 110 is coupled to a connection terminal. A dust cap 112 covers a hole in the diaphragm 106.
It is difficult to make one speaker driver that reproduces sound waves over the entire frequency range of human hearing. Speaker units therefore typically divide a wide frequency range among multiple drivers. Most high-fidelity speakers include more than one size driver. This, however, can increase size, cost, and complexity. Indeed, a design conflict exists between size and performance.
One prior-art method for attempting to achieve high-quality sound in a small-scale design, seen in conventional speakerphone and speaker/microphone designs using acoustic suspension speakers, is to use a sealed speaker enclosure with the required acoustic volume to meet the minimum performance values at the lowest frequency. The electronics and support elements are placed outside the speaker enclosure, and the total is contained within a second enclosure. The total product package volume is the sum of the speaker enclosure volume plus the electronics and support elements volume, increasing cost and size.
Other prior-art systems avoid solving the problem by sacrificing performance. One common approach is to discard an enclosed speaker entirely and let the speaker operate with an open back, which reduces volume, compromises low frequency performance, and increases distortion. These systems are sometimes enclosed, but are not completely sealed.